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Rockwool has long been one of the most popular hydroponic growing mediums. The vast majority of Rockwool used in the world is used for insulation purposes (much like fiberglass). However, adjusting the mineral content can substantially change the properties of Rockwool. In the early 1960s it was found that following several modifications to the manufacturing process Rockwool would support and, under the right handling practices, promote plant growth. This produced horticultural rockwool, which is what is sold as a hydroponic substrate.

Grodan, the leading distributer of Rockwool, produces Rockwool by melting basaltic rock and limestone to temperatures as high as 3000°F (1600°C), at which point they become lava. They are then put into a spinning chamber and are spun together into fibers, much like cotton candy. Immediately following spinning, a binder is added to the fibers and they are compressed and cured into large slabs. By adjusting the amount of pressure, the density of the media is adjusted. The large slabs can be cut into smaller slabs and propagation blocks for easy handling. The spun fibers are also formed into a granulated product, which can be handled in a manner similar to bales of peat.

Rockwool is an inorganic substrate; therefore it maintains its structure over a long period of time. In general, Rockwool holds more water per unit volume than the other inorganic substrates and therefore has a greater buffering capacity. Rockwool is inert, so it has no built in nutrition and does not add or take anything away from plants. It can be used in either recirculating or drain to waste systems, and with either synthetic or organic nutrients.

Advantages of Rockwool:

Retains Water – Since rockwool will easily give up water to the roots, even when it is almost dry, growers can allow more of the pore space in rockwool for air, while still maintaining a satisfactory supply of nutrient solution to the roots.

Holds Air – Rockwool holds at least 18 % air at all times (unless it is sitting directly in water), which supplies the root zone with plenty of oxygen.

Clean & Convenient – Rockwool holds together very well so it can’t spill. Rockwool also comes wrapped in plastic, which makes it easy to handle and keeps evaporation to a minimum.

Comes In A Variety Of Sizes And Shapes – From 1″ cubes designed for use in propagation, to 3″x12″x36″ slabs capable of holding the root systems of huge plants, rockwool comes in dozens of shapes and sizes making it a versatile growing medium. Rockwool also comes “Loose” so you can fill pots or containers of any size.

Rockwool Conditioning Tips*

When rockwool is new it contains some residual lime from production. This has led to a mistaken belief that rockwool is alkaline and that one has to continuously adjust pH. In fact, once the lime is flushed out, rockwool is pH neutral.

Immediately before use, flush the rockwool with a pH 5.5 solution. This is done to flush out the dissolved lime. The lime will make the pH value rise to 6.0. From this point onwards rockwool does not change the pH in any way. Most rockwool cubes will have presoak instructions on the packaging.

How to pH condition:

Saturate rockwool in no lower than pH 5.5 water for about half an hour to an hour, depending on the amount of rockwool you are conditioning. Higher quantities of rockwool will require longer flushing times to saturate evenly.

Remove and let drain to waste.

Flush through the rockwool with a normal nutrient solution at pH 5.5-6.0, just prior to planting.

There are also products such as Europonic Rockwool Conditioner that make the presoak process much easier by adjusting and stabilizing rockwool for maximum nutrient uptake. A unique blend of pH controls and minerals, use it for conditioning your rockwool before starting seed, clones or transplants. Use three ounces of Europonic Rockwool Conditioning Solution per gallon of water and mix thoroughly. Saturate dry rockwool with this mixture and let soak overnight.

It is important that you do not condition your rockwool with a solution at a pH lower than 5.5. If you do this, you can damage the actual fibers of the rockwool. If you use a pH 4.0 solution, you will find that your pH jumps all the way to 7.0. The lower the pH you use, the higher it jumps. If the fibers are damaged it can be difficult to re-establish a stable pH level, so never go below pH 5 with rockwool. To soak cubes, put them in a bucket filled with water. To soak slabs, cut a hole in the plastic bag they come in and fill it with water until totally saturated. After 24 hours, cut drainage slits in the bottom.

If handling rockwool in a dry state and working in confined spaces, always use a protective mask so that you aren’t breathing in the harmful dust. Although it is non-toxic, rockwool can cause skin irritation. Always wear a dust mask and gloves when handling dry rockwool. If skin irritation occurs, rinse the area with water.

San Diego Hydroponics & Organics is kicking off our annual charity drive event, Season of Giving, on September 10th! We will be collecting clothing, food and toys through December 14th to donate to three outstanding local non-profit organizations – Alpha Project, San Diego Food Bank and Toys for Tots.

Bring in your clothing, food and/or toy donation anytime during our Season of Giving to a SD Hydro location. We will be donating the collected goods in time for families to enjoy them during the holiday season! Please feel free to reach out to marketing@sdhydroponics.com if you have any questions about the donation process.

For the past three years SD Hydro has been asked to install, staff and manage the FarmScraper installation at the San Diego County Fair, located inside the CA Grown building. The purpose of the FarmScraper exhibit is to showcase the future of farming technology and focusing on environmentally friendly gardening practices. We look forward to this opportunity each year and we are always thinking up ways we can improve our systems and educational materials for the next year!

This year, the showcase of the exhibit was our vertical hydroponic system. The curved system was custom built by SD Hydro staff and is capable of growing 55 plants with a fraction of the amount of water used in traditional gardening practices. The vertical system utilizes a specific subset of hydroponics, called aeroponics, that uses mist to deliver water and nutrients to the plants roots. Aeroponic is the most water efficient out of all other hydroponic growing methods.

Our other hydroponic displays included a “floating” raft and Aeroflo system. All of the varieties of lettuce were donated by the Encinitas based commercial hydroponic farm, Go Green Agriculture.

Vertical aeroponic, raft system, Aeroflo

The FarmScraper once again displayed our “living wall” with around 75 hanging planters donated by Smart Pot. The living wall demonstrates how to use available space to efficiently grow food or plants in a “future” scenario where horizontal land could be scarce, especially in urban settings. We’d like to thank Olive Hill Greenhouses for donating the indoor plants that made our living walls lush and colorful. According to Olive Hill Greenhouses, indoor plants also, “…decrease the amount of indoor air pollution by reducing concentrations of formaldehyde and other volatile organic chemicals. Interiors with plants have 50% to 60% fewer airborne microorganisms and 20% less dust than interiors without plants; moreover plants are able to adjust transpiration rates, thereby stabilizing relative humidity to levels ideal for human health and comfort.”

This year we added a weekly seed planting activity as part of our exhibit. It was a huge hit! Everyone loved planting pumpkins in the biodegradable pots donated by Jiffy! We chose to start pumpkin seeds so they would be ready to harvest in late October.

Another fun addition to our exhibit was the 20 ft. interactive mural wall! Kids and grown-ups alike had a great time “leaving their mark” at the fair. Our mural was so popular we went through 4!

Planting a succulent wall can be an easy way to add character and color to your outdoor or indoor spaces. There are many types of vertical wall planters to choose depending on your space, budget and design goals. We knew we wanted to make a vertical planter for our “Drought Tolerant Plants” for our FarmScraper display at the San Diego County Fair. We chose to work with fabric wall planters because they are cost effective and matched the “unfinished” look of our FarmScraper. These fabric planters are ideal for outdoor spaces, covering large areas, and those working on a budget. After you select your wall planter, you will need to buy your plants.

We purchased our succulents from a local wholesale nursery that is open to the public. Plants from this type of nursery will cost far less than those at a larger chain store and will most likely be available in a wider variety. We selected two different sizes of plants as we were using two different wall hangers with different pocket sizes. Next you will want to select your soil.

Selecting a soil for succulents can be tricky. A high quality potting soil mix will usually be a good choice. For this planter, we chose to use Aurrora Innovation’s soilless medium because we knew it would hold moisture for the duration of the fair. Drought tolerant plants will do well in soilless mediums, such as coco mixed with perlite or sand, as long as they are watered and fed periodically. For this particular type of planter, we learned that you need to start with planting the bottom pockets first and then work your way up. After all of the pockets were planted, we gave each one a thorough watering using a Hudson sprayer, knowing that we wouldn’t have to water them again until the soil or grow medium is completely dried out.

Happy new year! We’re happy to say that our 2017 Season of Giving Charity Drive was a great success! Thank you to everyone who donated clothing, food and toys.

We were able to donate an entire pallet of gently used clothing to Alpha Project, a local organization that serves over 4,000 San Diegans each day. From the Alpha Project website, “Services offered include affordable housing, residential substance abuse treatment, supportive housing for people with special needs, basic and emergency services for the homeless, transportation assistance, mental health counseling, employment training, preparation and placement, education, outreach and prevention, and community services.” We’re very excited to keep working with Alpha Project on future endeavors and community projects!

In November we focused on collecting food to donate to the San Diego Food Bank. The food bank serves over a quarter million individuals EVERY month and accommodates about 24,000 volunteers every year. We were able to donate 214 pounds of food this year and we hope to go above and beyond that number next year.

Finally, in December, we collected donations for Toys for Tots, an organization run by the U.S. Marine Corps Reserve designed to bring new toys to less fortunate children. You, our customers, really showed the love for this drive! Every store was able to bring a sizable donation of new, unwrapped toys to local fire departments just in time for Christmas!